Diffraction at DØ Andrew Brandt University of Texas at Arlington E   Run IRun II Low-x Workshop June 6, 2003 Nafplion, Greece

Examples of Soft Diffraction  Modeled by Regge Theory  Non-perturbative QCD  No quantum number exchanged –Synonymous with exchange of a Pomeron

Examples of Hard Diffraction  Described by Different Models –Ingelman-Schlein based (q/g partonic structure of Pomeron) –BFKL-based (gluon ladder structure of Pomeron) –Soft Color Interactions (non-perturbative effects of standard QCD) Diffractively Produced Jets Diffractively Produced W

Particle Multiplicity Distributions

DØ Detector (Run I) EM Calorimeter L0 Detector beam (n l0 = # tiles in L0 detector with signal 2.3 < |  | < 4.3) Central Drift Chamber (n trk = # charged tracks with |  | < 1.0) End Calorimeter Central Calorimeter (n cal = # cal towers with energy above threshold) Hadronic Calorimeter Central Gaps EM Calorimeter E T > 200 MeV |  | < 1.0 Forward Gaps EM Calorimeter E > 150 MeV 2.0 < |  | < 4.1 Had. Calorimeter E > 500 MeV 3.2 < |  | < 5.2)

Why study Diffractive W Boson?

Data Samples Z boson sample: Start with Run1b Z ee candidate sample Central and forward electron W boson sample: Start with Run1b W e candidate sample

Multiplicity in W Boson Events   Minimum side Peak at (0,0) indicates diffractive W boson signal (91 events) DØ Preliminary Plot multiplicity in 3<|  |<5.2

W Boson Event Characteristics M T =70.4 E T =36.9 E T =35.2 Standard W Events Diffractive W Candidates E T =35.1 E T =37.1 M T =72.5 DØ Preliminary

Observation of Diffractive W/Z  Observed clear Diffractively produced W and Z boson signals  Background from fake W/Z gives negligible change in gap fractions Sample Diffractive Probability Background All Fluctuates to Data Central W( )% 7.7  Forward W( )% 5.3  All W( – 0.17)% 7.5  All Z ( )% 4.4  n cal n L0 Diffractive W and Z Boson Signals Central electron WForward electron W All Z n cal n L0 n cal n L0 DØ Preliminary

R D =  (W D ) /  ( Z D ) = R*(W D /W)/ (Z D /Z) where W D /W and Z D /Z are the measured gap fractions from this letter and R=  (W)/  (Z) = ±0.15 (stat) ±0.20 (sys)±0.10 (NLO) B. Abbott et al. (D0 Collaboration), Phys. Rev D 61, (2000). Substituting in these values gives R D = This value of R D is somewhat lower than, but consistent with, the non-diffractive ratio. DØ Preliminary W/Z Cross Section Ratio

Calculate  =  p/p for W boson events using calorimeter : Diffractive W Boson   data  E t i e y i /2E Sum over all particles in event: those with largest E T and closest to gap given highest weight in sum (particles lost down beam pipe at –  do not contribute Use only events with rapidity gap {(0,0) bin} to minimize non-diffractive background Correction factor derived from MC used to calculated data  DØ Preliminary

CDF {PRL (1997)} measured R W = (1.15 ± 0.55)% for |  |<1.1 where R W = Ratio of diffractive/non-diffractive W (a significance of 3.8  ) We measured ( –0.17)% for |  |<1.1 No problem right? Well… CDF corrects data for gap acceptance using MC and get 0.81 correction, so get an uncorrected value (0.93 ± 0.44)%, which is still consistent with our uncorrected data value. Our measured gap acceptance is (21 ± 4)%, so our corrected value is 5.1%!! Comparison of other gap acceptances for central objects from CDF and DØ using 2-D method: DØ central jets 18% (q) 40%(g) CDF central B 22%(q) 37% overall CDF J/  29% It will be interesting to see Run II diffractive W boson results! DØ/CDF Comparison

  E Soft Diffraction and Elastic Scattering: Inclusive Single Diffraction Elastic scattering (t dependence) Total Cross Section Centauro Search Inclusive double pomeron Search for glueballs/exotics Hard Diffraction: Diffractive jet Diffractive b,c,t, Higgs Diffractive W/Z Diffractive photon Other hard diffractive topics Double Pomeron + jets Other Hard Double Pomeron topics Rapidity Gaps: Central gaps+jets Double pomeron with gaps Gap tags vs. proton tags Topics in RED were studied with gaps only in Run I 1000 tagged events expected in Run II DØ Run II Diffractive Topics

Run II Rapidity Gap System  Use signals from Luminosity Monitor (and later Veto Counters) to trigger on rapidity gaps with calorimeter towers for gap signal  Use calorimeter at Level 2 to further refine rapidity gaps VC: 5.2 <  < 5.9 LM: 2.5 <  < 4.4

Calorimeter Energy for Gap Triggers DØ Preliminary E North LM Veto North E South LM Veto North E North LM Veto South E South LM Veto South Trigger on gap in Luminosity Monitor (LM) + two 25 Gev jets; Sum EM energy DØ Preliminary

Leading Jet E T Inclusive Jets North Gap Jets South Gap JetsDouble Gap Jets E T (GeV) DØ Preliminary

Forward Proton Detector Layout  9 momentum spectrometers comprised of 18 Roman Pots  Scintillating fiber detectors can be brought close (~6 mm) to the beam to track scattered protons and anti-protons  Reconstructed track is used to calculate momentum fraction and scattering angle –Much better resolution than available with gaps alone  Cover a t region (0 < t < 4.5 GeV 2 ) never before explored at Tevatron energies  Allows combination of tracks with high-p T scattering in the central detector D S Q2Q2 Q3Q3 Q4Q4 S A1A1 A2A2 P 1U P 2I P 2O P 1D p p Z(m) D2 D Veto Q4Q4 Q3Q3 Q2Q2

FPD Detector Setup  6 planes per detector in 3 frames and a trigger scintillator  U and V at 45 degrees to X, 90 degrees to each other  U and V planes have 20 fibers, X planes have 16 fibers  Planes in a frame offset by ~2/3 fiber  Each channel filled with four fibers  2 detectors in a spectrometer 0.8 mm 3.2 mm 1 mm mm U U’ X X’ V V’ Trigger

Tagged Elastic Trigger NO HITS IN LMN OR LMS OR VCN OR VCS NO EARLY HALO HITS IN A1U-A2U, P1D-P2D IN TIME HITS IN A1U-A2U, P1D-P2D A1UA2U P2DP1D P Pbar Halo Early Hits  Approximately 3 million elastic events recorded  About 1% (30,000) pass multiplicity cuts –Multiplicity cuts used for ease of reconstruction and to remove halo spray background from Tevatron 1 or 0 hits in each of 12 planes of the PD spectrometer Each frame of both PD detectors needs a valid segment (i.e. 6 segments total) Segments turned into hits and then reconstructed into tracks LM VC

Segments to Hits y x 10  u x v Segments (270  m)  Combination of fibers in a frame determine a segment  Need two out of three possible segments to get a hit –U/V, U/X, V/X Can reconstruct an x and y  Can also get an x directly from the x segment  Require a hit in both detectors of spectrometer

 =  p/p should peak at 0 for elastic events!! Dead Fibers due to cables that have since been fixed P1D P2D beam Y X Y Reconstructed  beam Initial Reconstruction DØ Preliminary

Spectrometer Alignment  Good correlation in hits between detectors of the same spectrometer but shifted from kinematic expectations –3mm in x and 1 mm in y P1D x vs. P1D x (mm) P1D y vs. P2D y (mm) DØ Preliminary

t distribution Before alignment After alignment Gaussian fit After alignment correction,  peaks at 0 (as expected for elastics); MC  resolution is (including z smearing and dead channels), data is 0.015, 1.15 times larger The t distribution has a minimum of 0.8 GeV 2 ; t min is determined by how close the pots are from the beam, shape is in rough agreement with expected angular acceptance from MC. Elastic Data Distributions DØ Preliminary

TDC Timing from Trigger PMTs From TDCs : 18ns = (396ns – L1/c) – L1/c 4ns = (396ns – L2/c) – L2/c  L1 = 56.7 m; L2 = 58.8 m Tevatron Lattice: L1 = 56.5m; L2 = 58.7m TOF: 197ns 190ns t p – t p = 18ns t p – t p = 4ns DØ Preliminary

TDC Resolution  Can see bunch structure of both proton and antiproton beam  Can reject proton halo at dipoles using TDC timing D1 TDC D2 TDC pbar p DØ Preliminary

Summary and Future Plans  Run II analysis still in early stages  Early FPD stand-alone analysis shows that detectors work  FPD is now integrated into DØ readout  Commissioning of FPD and trigger in progress  Definition of rapidity gaps in Run II detector underway  Tune in next year for first FPD physics results